The present invention relates to the field of earth boring and, more particularly, the directional control of horizontal earth boring tools.
It has long been recognized by utility companies that installing utility lines underground is safer and more esthetically pleasing, generally producing less of an environmental impact than above-ground or excavated trench type installation methods. The most common means of installing underground lines by the cut and cover technique where a ditch is first dug in the area, the utility line is installed, and the ditch covered. While the cut and cover technique is satisfactory for new construction areas, built up areas of existing construction require a different method so as not to disturb the existing structures and traffic areas.
Consequently, a number of earth boring devices have been proposed for boring through unconsolidated material such as soil. Previous horizontal boring equipment has been plagued with the serious problem of the inability to exercise adequate control over the direction of the drill string. Thus, many prior art devices have lacked the capability of redirecting the drill string along the proper horizontal path should it deviate from that correct path. Moreover, many of the prior art devices lack optimum abilities to advance around a curve.
In one such earth boring device of the prior art, a high pressure fluid is conveyed to an angled nozzle to a section of rotating pipe. Fluid ejected from the nozzle performs the earth boring operation. When the tool is to be advanced around a curve, rotation of the pipe is stopped so that the angled nozzle is pointed in the proper direction. The tool is then pushed without rotation until the proper amount of curvature is obtained. The patent to Geller, et al., U.S. Pat. No. 4,787,463, is representative of this type of earth boring device.
In another earth boring device of the prior art, as represented by the patent to Adkins, et al. U.S. Pat. No. 3,526,285, a horizontal auger includes a tilting auger head which carries a pilot bit. The tilting of the auger head is achieved by use of a wobble plate and universal joint assembly oriented on a casing surrounding the auger itself. During the boring operation, earth is carried conveyed by the auger blades through the casing. When it is necessary to change the direction of the auger earth boring device, the wobble plate is tilted about a single axis so that the auger head and pilot bit are also tilted. In order to achieve multiple degree of freedom movement of the earth boring device, it is necessary that the auger casing be rotated to an appropriate position to re-orient the wobble plate tilt axis thereby controlling the direction of motion of the boring device.
None of the above described devices provides a mechanical direction control for a steerable earth boring auger that is completely enclosed, rather than exposed to the earth during the boring operation. There is a need for providing a reliable steering mechanism for a steerable earth boring device, that utilizes mechanical forces, rather than fluid forces to perform the steering operation. There is also a need for a device that permits multiple degree of freedom tilting or steering of the earth boring auger in a simple and easily maintained mechanism.